Toward unraveling the mechanisms responsible for the formation of ultrafine grained microstructure during tempering of cold rolled martensite

Najafi, Mahnaz; Mirzadeh, Hamed; Alibeyki, Mohammad

doi:10.1016/j.msea.2016.06.024

Cited by 20 publications

(16 citation statements)

References 8 publications

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“…Different techniques have been used for grain refinement of DP steels. The intercritical annealing of cold‐worked martensite or ultrafine grained (UFG) ferrite‐carbide aggregate, fast and ultrafast heating, ultrafast cooling (UFC), Deformation‐induced ferrite transformation (DIFT), and severe plastic deformation have been recently practiced. Most of these techniques are based on prior deformation and need rolling facilities or more complicated and expensive deformation routes.…”

Section: Introductionmentioning

confidence: 99%

Refinement of Banded Structure via Thermal Cycling and Its Effects on Mechanical Properties of Dual Phase Steel

Ghaemifar

Mirzadeh

2018

steel research int.

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The microstructural refinement by thermal cycling and its effects on the enhancement of mechanical properties and work-hardening response of a typical C-Mn dual phase (DP) steel having the banded ferritic-martensitic morphology is evaluated. It is revealed that the band spacing is reduced by decreasing austenitization temperature and applying thermal cycles to intercritical region, where a saturated spacing will be reached. This results in the enhancement of work-hardening capacity of DP steels as demonstrated based on the instantaneous (incremental) work-hardening rate exponents, modified Crussard-Jaoul analysis, and evaluating the yield ratio after tensile tests. These observations justify the potential of this simple heat treatment route for microstructural control of DP steels. Figure 8. a) Dependence of UTS and total elongation on band spacing and b) Dependence of yield ratio and UTS-YS on band spacing.www.advancedsciencenews.com www.steel-research.de steel research int. 2018, 89, 1700531

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Section: Introductionmentioning

confidence: 99%

Refinement of Banded Structure via Thermal Cycling and Its Effects on Mechanical Properties of Dual Phase Steel

Ghaemifar

Mirzadeh

2018

steel research int.

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“…6) consists of fine ferrite grains of ∼ 0.9 µ m originated from the martensitic regions of DP1 steel, and large fine ferrite grains of ∼ 8 µ m originated from the ferritic regions of DP1 steel. The development of fine ferritic structure in the cold-rolled martensitic microstructure has been recently studied by the present authors [37], and a form of continuous recrystallization was found to be responsible for microstructural changes [37].…”

Section: Bimodal-sized Ferrite Structure (Bimodal)mentioning

confidence: 83%

“…The DP1 sheet was cold rolled with a reduction in thickness of 70 %. Then, it was subjected to tempering at 550 • C for 45 min to obtain a steel with bimodal sized ferrite (known as Bimodal steel in this work), where the choice of tempering temperature and time was based on the recent results reported by Najafi et al [37] for obtaining an ultrafine grained (UFG) ferrite-carbide aggregate from the cold-rolled martensite. Afterwards, the sheet was heated to 775 • C for holding time of 1 min and then water quenched to produce another dual phase ferritic-martensitic structure (DP3).…”

Section: Processingmentioning

confidence: 99%

The effects of primary thermo-mechanical processing routes and intercritical annealing on the mechanical properties of st37 low carbon steel

Alibeyki¹,

Mirzadeh²,

Najafi³

2018

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The effect of thermo-mechanical processing routes on the microstructure and mechanical properties of st37 low carbon steel was studied. Several dual phase (DP) ferritic-martensitic steels were produced by intercritical annealing of the martensitic, cold-rolled martensitic, and bimodal-sized ferritic microstructures. The latter microstructure was produced by subcritical tempering of cold-rolled DP steel to develop an aggregate of ultrafine and large ferrite grains. The DP steel obtained by intercritical annealing of cold-rolled martensite was shown to exhibit better strength-ductility balance compared with that obtained by intercritical annealing of the as-quenched martensite due to much finer microstructure and enhancement of work-hardening behavior in the former. The bimodal-sized ferritic structure showed high yield stress, yieldpoint elongation, and less pronounced work-hardening regime. The DP steel obtained by intercritical annealing of bimodal-sized ferritic structure exhibited inferior strength-ductility tradeoff compared with that obtained by intercritical annealing of cold-rolled martensite due to the coarser microstructure in the former. Conclusively, it is possible to enhance the mechanical properties of st37 low carbon steel by simple processing routes. K e y w o r d s : dual phase steels, microstructure, mechanical properties, strain hardening rate

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“…While the focus of the SPD techniques is on the applied high strain, there is an increasing interest to use advanced thermomechanical processing routes for grain refinement with less required strains, where these techniques have been discussed by Tsuji and coworkers [12,13]. In this respect, lath martensite characterized by pockets, blocks, and laths with its high dislocation density has been reported to be quite advantageous by Najafi et al [14], Wang et al [15], Azizi-Alizamini et al [16], and Morito et al [17].…”

Section: Introductionmentioning

confidence: 99%

Tempering of deformed and as-quenched martensite in structural steel

Najafi

Mirzadeh

Alibeyki

2019

J min metall B Metall

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Annealing of deformed martensite (high-temperature tempering) in St37 steel was studied. Different reductions in thickness were considered and compared with the behavior of as-quenched martensite during tempering. tempering of the asquenched martensite was accompanied by the formation of carbide particles, incomplete disappearance of the lath martensite morphology, and continuous decrease in hardness until reaching low values. However, during tempering of the cold rolled martensite, the precipitation of carbides in the lamellar structure, development of distinct equiaxed ultrafine grains through a continuous recrystallization mechanism, and a sudden hardness drop were characterized. the importance of cold rolling reduction and its amount were also discussed.

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Toward unraveling the mechanisms responsible for the formation of ultrafine grained microstructure during tempering of cold rolled martensite

Cited by 20 publications

References 8 publications

Refinement of Banded Structure via Thermal Cycling and Its Effects on Mechanical Properties of Dual Phase Steel

Refinement of Banded Structure via Thermal Cycling and Its Effects on Mechanical Properties of Dual Phase Steel

The effects of primary thermo-mechanical processing routes and intercritical annealing on the mechanical properties of st37 low carbon steel

Tempering of deformed and as-quenched martensite in structural steel

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